The present invention is based on technical knowledge about ‘forward-facing rowing’ and ‘oscillating foil’ so as to safely secure a front view and improve energy efficiency of propulsion when a boat is propelled by using human power.
The most common example of the forward-facing rowing may be found in narrow beam boats having a sharp boat body such as a kayak or a canoe. However, in case of a wide beam boat having larger width, since a distance between its rider and the water surface outside the boat body is distant, a pivot may be positioned at a middle portion of each oar. Furthermore, since such a boat greatly undergoes propulsion resistance, the rider may generate propulsion force through a motion that pulls a handle of the oar backward than a motion that pushes the handle of the oar forward. The pulling motion may be converted in direction by the pivot, and thus, the boat may be accelerated in a direction opposite to the rider's eyes (backward-facing rowing).
Thus, in order to enable the rider to have a forward-facing rowing in the wide beam boat having the large width, additional ideas are necessary in addition to the installation of the pivot. The simplest solution of the ideas may be an “L-shaped oar”, in which a middle portion of an oar's loom is bent. When the oar has a shape in which the oar extends from the handle in a width direction of the boat body to meet a side of the boat body and then extends backward in a longitudinal direction of the boat body so that the extending end is coupled to a plate-shaped foil, the forward and backward movement of the rider's arm may be converted into a left and right oscillating motion of the foil to generate propulsion force as if a fish moves a tail fin thereof.
The oscillating foil may be chosen as best technology in the above-described means that is capable of “generating the propulsion force like a fish” (see Robotic Design for SHOAL—Swimming mechanism [on-line], SHOAL Project Consortium, 2012.) Explaining a configuration and operation of a basic mechanism for realizing the oscillating foil mechanism with reference to FIG. 1, a first pivot 11 is disposed on a front end of an oscillating crank 32 having a predetermined length, and a plate-shaped foil 12 is coupled to a rear end of the oscillating crank 32 to allow the oscillating crank 32 to oscillate about the first pivot 11. As a result, the foil 12 pushes water backward to generate propulsion force F.
In addition to these basic components, a second pivot 13 is additionally disposed on a front portion of the foil 12 to allow the foil 12 to relatively rotate with respect to the oscillating crank 32, thereby more improving propulsion efficiency. Explaining a specific operation principle, when rotating force is applied to the first pivot 11 in a counterclockwise direction in the idle state of the oscillating crank, the foil 12 rotates about the second pivot 13 in a clockwise direction while largely moving along a rear end of the oscillating crank 32 and then is stopped at a limited angle β. Thereafter, the foil 12 obliquely pushes water until the oscillating crank 32 reaches a limited angle α.
When the oscillating crank 32 switches its direction to start the rotation again in the clockwise direction, the foil 12 rotates in a counterclockwise direction and stops at a limited angle. Then, the foil 12 pushes water until the oscillating crank 32 reaches the limited angle.
That is, the foil 12 primarily largely oscillates about the first pivot 11, and simultaneously, secondarily flaps in small about the second pivot 13 to generate the propulsion force F.
Here, it is preferable that the first pivot 11 and the second pivot 13 provide rotation axes that are perpendicular to the water surface to prevent the boat body from pitching due to the oscillation of the foil 12.
According to the advanced researches about an oscillating foil propulsion mechanism, propulsion efficiency can be increased by making the end portion of the foil 12 flexible. (see H. Yamaguchi et al., “Oscillating Foils for Marine Propulsion”, The 4th International Society of Offshore and Polar Engineering Conference, vol. 3, 1994, pp. 539-544.)
Hereinafter, the prior arts, which are combinations of above-mentioned L-shaped oar and the oscillating foil mechanism, will be introduced using the above-mentioned terms.
The most impressive technology is U.S. Pat. No. 4,867,718 (1989 Sep. 19) to Stephen Dupont. Characteristically, two hinges, a ‘sweep hinge’ that corresponds to the first pivot by providing a vertical rotation axis at the bent part of L-shaped oars and a ‘teeter hinge’ that has a horizontal rotation axis, are coupled simultaneously and the two hinges may be involved in the entire movement of the oar at the same time. Here, in a coupling structure between the oscillating crank and the foil, the position of the second pivot is retreated toward a central portion of the foil, not to the front end of the foil. By doing this, it has the effect of accelerating the secondary flapping motion of the foil. U.S. Pat. No. 4,867,719 (1989 Sep. 19) filed by the same inventor discloses a feature in which a sliding outrigger is added to the components of the foregoing invention.
Thereafter, according to U.S. Pat. No. 6,964,589 (2005 Nov. 15) by Roger Lin, by transmitting the rider's arm movement to a rear side of a boat body using a power transmission device, the foil can perform flapping motion without colliding with the boat body even without an outrigger. In addition, the oscillating crank is obliquely dropped from a position higher than the water surface of the stern to minimize its submerging portion.
Thereafter, Jack Parker introduced the most simplified mechanism that is imaginable in corresponding technical fields by coupling the foil directly to the first pivot through U.S. Pat. No. 7,396,267 (2008 Jul. 8). U.S. Pat. No. 8,419,487 (2013 Apr. 16) filed by the same inventor discloses a feature in which the first pivot is moved from the inside to the outside of the boat body.